It is currently 23 Feb 2018, 19:56

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If f(x) = x^3 + kx^2 − 4x, what is the value of k?

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 43892
If f(x) = x^3 + kx^2 − 4x, what is the value of k? [#permalink]

Show Tags

New post 06 Aug 2017, 00:04
Expert's post
1
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

58% (01:45) correct 42% (01:48) wrong based on 42 sessions

HideShow timer Statistics

Manager
Manager
avatar
B
Joined: 02 Nov 2015
Posts: 174
GMAT 1: 640 Q49 V29
Premium Member CAT Tests
Re: If f(x) = x^3 + kx^2 − 4x, what is the value of k? [#permalink]

Show Tags

New post 06 Aug 2017, 00:56
Statement 1 alone is sufficient IMO.
As per statement 1: -f(-k) yields x^3-kx^2+4x.
So x^3+kx^2+4x=x^3-kx^2+4x.
Which ultimately yield 0.

So answer.
Statement 2 gives different values of K.

Sent from my Lenovo TAB S8-50LC using GMAT Club Forum mobile app
Director
Director
User avatar
P
Joined: 18 Aug 2016
Posts: 628
Concentration: Strategy, Technology
GMAT 1: 630 Q47 V29
GMAT 2: 740 Q51 V38
GMAT ToolKit User Premium Member Reviews Badge
Re: If f(x) = x^3 + kx^2 − 4x, what is the value of k? [#permalink]

Show Tags

New post 06 Aug 2017, 02:40
Bunuel wrote:
If f(x) = x^3 + kx^2 − 4x, what is the value of k?

(1) f(k) = −f(−k)
(2) f(f(2)) = 0


(1)
\(f(k) = 2k^3 - 4k = -f(-k) = -4k\)
\(k^3 = 0\)
\(k=0\)

Sufficient

(2)
\(f(2) = 4k\)
\(f(f(2)) = 80k^3 -16k = 0\)
\(k = 0,+1/\sqrt{5}, -1/\sqrt{5}\)
Not sufficient

Hence A
_________________

We must try to achieve the best within us


Thanks
Luckisnoexcuse

Re: If f(x) = x^3 + kx^2 − 4x, what is the value of k?   [#permalink] 06 Aug 2017, 02:40
Display posts from previous: Sort by

If f(x) = x^3 + kx^2 − 4x, what is the value of k?

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.